Floristic Kingdoms

Floristic Kingdoms


large aggregates of floras that are related to each other in origin and that formed on certain areas of the earth. Identification of a floristic kingdom is based primarily on paleogeographic factors (beginning for the most part from the Cretaceous period) and on current soil and climatic factors. Each kingdom has complexes of endemic plant families and genera, whose origin and distribution in the course of a long geological history occurred within the boundaries of the kingdom. Floristic kingdoms are divided into units of lower rank. Although botanists differ in their division of the earth’s surface into floristic kingdoms, there is fundamental agreement about the basic outlines.

The most extensive floristic kingdom is the Holarctic kingdom, which occupies the entire nontropical portion of the northern hemisphere, southward as far as the Cape Verde Islands, the northern parts of the Sahara and the Arabian Peninsula, the Persian Gulf, the southern slopes of the Hindu Kush and the Himalayas, and the southernmost part of China. In North America the region extends as far south as the northern parts of the Meseta Central and the Gulf of Mexico. Historically, the floras of Ho-larctica are associated with the ancient Paleogene-Neogene Arctic Tertiary floristic complex (and its derivatives) and with the American Madro-Tertiary floras. Connections with tropical floras proper have long been circumscribed by the extensive Tethys basin, whose isolating role resisted the congruence of the climatic conditions of southern Holarctica with those that are strictly tropical.

The flora of the Holarctic region is highly differentiated and is therefore divided into a number of floristic regions. The Arctic region has meager floras with a predominance of plants from the Gramineae, Cyperaceae, Cruciferae, Caryophyllaceae, and Compositae families. The Boreal region is characterized by a prevalence of coniferous trees and by an abundance of species of the Gramineae, Cyperaceae, and Compositae families. The Middle European region has a predominance of deciduous trees (forests of the temperate type) and an abundance of species of the Gramineae, Compositae, Rosaceae, and other families common to Holarctica.

The Mediterranean region is richly represented by the Compositae, Papilionaceae, Gramineae, Cruciferae, Labiatae, Caryophyllaceae, and Umbelliferae families. Its flora is highly differentiated over space, and progressive endemism is marked. The Central Asiatic region has a relatively poor flora that resembles that of the Mediterranean and Boreal regions, as well as that of the East Asiatic region, which has preserved many features of Arctic Paleogene-Neogene species associated with the development of progressive endemism. The basis of the flora of the California (Sonora) and Appalachian regions is relicts of the Paleogene-Neogene and Madro-Paleogene-Neogene complexes; there are elements of progressive endemism.

The Palaeotropical floristic kingdom extends southward from the Holarctic kingdom (in the eastern hemisphere), to the subtropics of southern Africa and to the islands of the Indian and Pacific Oceans. The flora is rich and highly differentiated. Predominant are the pantropical families, which are distributed equally in the Old and New Worlds (for example, palms and orchids). Particularly widespread are Rubiaceae, Euphorbiaceae, Arecaceae, Orchidaceae, Melastomaceae, Araceae, Moraceae, Lauraceae, and a number of groups of tubuliflorous plants. Cosmopolitan families and species include Gramineae, Leguminosae, and Compositae. There are only a few endemic families, for example, Dipterocarpaceae and Pandanaceae. The species composition of the floras is rich, especially in regions with a predominance of forest vegetation.

Because of the richness and differentiation of the floras of the Palaeotropical kingdom, the following regions are distinguished: Sahara-Sind, Sudan-Zambezi, Guinea-Congolese, Kalahari, Cape, Madagascar, Hindustani, Indo-Chinese, Malayan, Papuan, Hawaiian, and Polynesian.

The Neotropical kingdom extends from Southern California and the Bahamas to 41° S lat. The flora is characterized by the presence of a great number of cosmopolitan families (Orchidaceae, Compositae, Leguminaceae, Gramineae) and pantropical families (Arecaceae, Myrtaceae, Euphorbiaceae, Rubiaceae). The families Cactaceae and Bromeliaceae are endemic. Changes in the richness of the floras depend principally on climatic conditions: for example, moist, hot forest regions of the equatorial zone with diverse species composition change in subtropical latitudes and in the mountains. The following regions are distinguished: Caribbean, Orinoco, Amazon, Brazilian, La Plata, and Andean.

The Southern floristic kingdom occupies the continent of Australia, Tasmania, New Zealand, the southernmost portions of South America, the subantarctic islands, and Antarctica. Most unique is the flora of Australia, which includes Myrtaceae (in particular, eucalyptus), Proteaceae, Mimosaceae, Epacridaceae, Goodeniaceae, Restionaceae, and Casuarinaceae. The following regions are distinguished: Australian (a number of botanists consider this as a floristic kingdom), New Zealand, New Caledonian, and Magellan-Antarctic.


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